During the development of IP over ATM (IPOA) technology, the multi-protocol label switching (MPLS) technology has emerged. The MPLS is a label forwarding technology for realizing Layer 3 routing and Layer 2 switching, which has been widely accepted. The operation principle of the MPLS is that one label is provided to each IP data packet, and the label determines a path and priority of the data packet. The length of the label is fixed, and is merely meaningful between the two devices for performing information switching. Before the data packet is forwarded to a path, a router compatible with the MPLS merely reads the label of the data packet, without reading an IP address and header of each data packet (thus, the network speed is accelerated), and then sends the data packet to be transferred in a virtual circuit of a frame relay or ATM, and rapidly transfers the data packet to a next hop. After receiving the data packet, a next hop router switches the label of the data packet into a label between the current router and the next hop and then forwards the data packet, and so forth, till the data packet is transferred to a destination router. As merely the label is read, and the IP address and the header of each data packet are unnecessary to read, the delay of the data packet is reduced, and meanwhile, as the transferred data packets are classified according to the quality of service (QoS) provided by the frame relay and ATM switch, the network service quality is improved significantly, and diversified services are provided.
The MPLS is an integrated IPOA technology, that is, integrating a routing function to the frame relay and ATM switch, in which data packets are transferred through a virtual circuit, and hardware switching is merely executed at OSI Layer 2 (data link layer) (software routing at Layer 3 (network layer) is replaced), which integrates the IP routing with the Layer 2 label switching. Thus, the Internet routing problem is solved, the delay time when the data packet is transferred is reduced, and the network transmission speed is increased, so that the MPLS is applicable to transfer multimedia information.
In view of the above, since the MPLS adopts label switching, the network router performs a forwarding operation simply after distinguishing the label, so as to realize the forwarding technology of Layer 3 routing and Layer 2 switching. However, the routing device of the MPLS does not perform routing based on content information of the data packet to be forwarded, so that the routing forward based on the content cannot be realized.